Method of melting pitch and producing pitch products



y 1934- s. P. MILLER ET AL 57,469

METHOD OF MELTING PITCH AND PRODUCING PITCH PRODUCTS Filed June 3, 1930 an?! uw'zenl INVENTORS .5, wzzfi 7, 3: r 142444 ATTORNEYS Patented May 8, 1934 AT FFEFCE METHOD OF MELTING PITCH AND PRODUC- ING PITCH PRODUCTS Application June 3, 1930, Serial No. 459,060

5 Claims.

This invention relates to a method of melting powdered high melting point pitch and producing pitch products. It includes both the method and apparatus for carrying it out.

According to this invention, pitch of high melting point available in solid form from any previous operation, is melted in an externally heated still or vessel by heating it with a liquid bituminous material such as tar, which may simultaneously be distilled, or with pitch resulting from the distillation of tar, or with any such bituminous material with which the melted pitch forms a substantially homogeneous blend.

Before being melted in this manner, the solid high melting point pitch is advantageously reduced to a more or less subdivided form such as chips, granules, powder or the like, if not already in such form.

The melting or remelting of solid high melting pitches (e. g. of melting points of 300 F. to 4:09 F.

or higher) is an operation of great practical diniculty. It has never to our knowledge been successfully carried out on a large commercial scale by any of the usual melting methods. If an attempt is made to melt such pitch by charging it to a still or vessel which is heated by the external application of heat in the usual manner, that portion of the pitch which touches the walls of the still will become overheated and will be decomposed and partially carbonized. This invention provides one advantageous method of melting or dissolving such high melting point pitches.

The still employed for carrying out this invention is a still capable of holding a large body of tar or pitch. It is an externally heated still, i. e. a still heated by a fire-box, a hot oil-coil, a hot metal bath or the like. It is provided with means for introducing the solid pitch. In order to keep the contents of the still uniform at all times, the still is advantageously connected with a circulating system for continuously drawing 01f a small portion of the liquid contents of the still and returning at least a portion of the material drawn oiT to another part of the still. By continuously circulating liquid in this manner, the contents of the still are continuously agitated. Stirring means may be provided in the still to prevent the accumulation of solid or partly solid pitch on the bottom of the still where necessary.

The melting of the solid pitch may be carried out as a continuous process or as a batch operation. The solid pitch is not added to the still until the contents of the still are brought to a temperature sufficient to dissolve or melt solid pitch in a relatively short period of time. The

solid pitch is added to the still gradually either A I in a continuous stream or in small increments.

To start the process tar may be introduced into the still until the still contains a considerable body of the material to be distilled. This tar is heated by applying heat externally to the still either by means of a fire-box under the still or other suitable means such as a pipe coil in the bottom of the still through which a heating fluid is passed. The application of the heat to the still is so regulated as to prevent local over-heating and undesirable decomposition of the contents of the still. After the contents of the still have been heated to a temperature sufiicient to melt the solid pitch, the pitch is gradually added and dissolved therein.

When the operation is carried out as a batch operation, a portion of the contents is continually withdrawn from the still and pumped through a pipe which returns it to a difierent part of the still from that from which it was withdrawn. The vapors produced by distillation of the tar are drawn oii from the still and condensed in any suitable manner. After lower boiling oils are distilled from the tar and the tar has been brought to a temperature sufficient to melt the solid pitch in a relatively short period of time, the addition of the solid pitch to the still may be commenced. The addition of solid pitch to the still may be begun before the distillation of the tar has been completed and the solution or blend of the pitch in the tar residue and distillation of the tar or pitch to produce pitch may be carried on simultaneously. Where pitch of high melting point is to be produced, for example, after the contents of the still have been heated to a temperature at which the solid pitch will readily melt, for example, a temperature of 250 C., introduction of solid pitch into the still may be commenced and the solid pitch may be introduced in such quantities as to control the temperature of the contents of the still and thus to control the distillation. The temperature at which the solid pitch is first introduced into the still will vary, depending upon the melting point of this pitch, and it need not be introduced as soon as the contents of the still reach a temperature at which the pitch will readily melt, but the contents of the still may be heated considerably above this point before the pitch is first introduced. The addition of solid high melting pitch to the still is continuous and distillation is carried on until a product of desired characteristics is obtained. The addition of pitch to the still may be discontinued before the completion of the distilling operation, or by reducing the rate at which heat is supplied to the still or by increasing the rate at which solid pitch is added to the still, the temperature may be so controlled that distillation ceases before th introduction of solid pitch into the still is discontinued.

As an alternative method, the distillation may he brought to completion or substantial completion before any solid pitch is introduced into the still and where desirable the solid pitch may be introduced into the still in such quantities that the temperature of the contents of the still is lowered below the boiling point of the contents. The distillation may be terminated simu1taneously with the first introduction of solid pitch into the still. The sensible heat of the contents of the still and of the apparatus itself, viz. the still walls and the fire-box Where a fire-box is employed in connection with the still, etc. may be sufllcient to melt the solid pitch. In this case, the supply of h at to the still may be discontinued during the addition of pitch to the still so that the pitch is melted by this sensible heat. Where desirable, the addition of heat to the still may be continued even after all of the solid pitch is added to the still and the heating may be continued as long as desirable. When the solid pitch is dissolved or melted solely by the sensible heat contained in the pitch and apparatus, the temperature at which the pitch product produced in the still is withdrawn from the still is lower than that at which the pitch produced in the still would otherwise be withdrawn. Since ordinarily the heat contained in freshly produced pitch as it is withdrawn from the still is dissipated, the melting of the pitch by the sensible heat effects fuel economy. The thinly fluid pitch may be drawn off of the still and be used in any desired manner.

When the operation is carried out as a continuous operation, the melting of the solid pitch in the hot contents of the still may be carried on simultaneously with the distillation of the tar and production of pitch therefrom. On the other hand, solid pitch may be continuously added to melted pitch or" the same or similar composition in a still or vessel, heated sufliciently to melt the added pitch, but not to effect substantial distillation, and the melted product continuously with drawn. In starting such a continuous operation, the tar or melted pitch from another operation is charged to the still and the contents of the still are advantageously brought to a temperature at which the process is to be carried out before solid pitch is added to the still and then the solid pitch is introduced into the still continuously at a uniform rate and sufficient heat is supplied to the still to melt the solid pitch.

When tar is distilled, the tar introduced into the still be distilled to pitch of high melting point, for example, a pitch of substantially the same melting point as that of the solid pitch. The product drawn off from the still will then be a melted pitch of substantially the same melting point as the melting point of the solid pitch in- I troduced into the still and will comprise the solid pitch and pitch resulting from the distillation of the tar. This high melting point pitch may then be blended with a flux to produce road tar, roofing pitch, etc., or it may be treated in any desired manner.

A large volume of pitch is disposed of as road tars. The demand for road tars is small during the winter months and larger during the spring and summer months. When the demand is small, the tar distiller may continue to operate and produce distillate and store the pitch produced as solid high melting point pitch. When the demand for road tars then increases, he may add the solid pitch to the still in which he is distilling tar and produce in the still a high melting point pitch which he may then blend with flux to produce road tar.

The solid high melting point pitch may be pitch resulting from the distillation of any tar the distillation of which can be carried out to produce a high melting point pitch, such as coke oven tar, gas house tar, a carburetted water gas tar, etc. This pitch may be produced by distillation in an ordinary direct fired still with inert gas recirculation in the still, or by distillation in the form of a fine intense spray in a current of hot inert gases such as coal distillation gases or steam, or in a tar heater, etc. The tar distilled in the still may be a coal tar such as coke oven tar or gas house tar or it may be carburetted water gas tar, etc.

The product from the still in which the solid pitch is melted and the tar is distilled may be blended with a coal tar such as coke oven tar or gas house tar where further blending is considered desirable.

In the production of road tars at the present time, it is customary to blend coke oven tar with gas house tar in the proportions necessary to produce a pitch of desired free carbon content and then distill this blended tar to the desired melting point. When tars are distilled to pitch with a melting point of 105 R, an oil yield of 13 to 16% is obtained.

When colre oven tar is distilled to pitch of sufficiently high melting point, some decomposition takes place and the carbon content increases. Such pitch may be blended with coke oven tar or a pitch of lower melting point produced from coke oven tar to give directly a pitch product of the high carbon content demanded for road tar. Road tar can thus be produced entirely from coke oven tar without the addition of gas house tar or other tar of high carbon content.

Road tar produced according to this invention by dissolving high melting point pitch in tar which is only topped, for example, tar-which is distilled to a flux of 60 seconds Engler viscosity (100 cc. at 100 C.) preferable to road tar produced by the straight distillation of a mixtureof coke oven tar and gas house tar to the same melting point, because the blended product contains a lower percentage of low boiling oils, for example oils that will distill below 355 C. A road tar with a low content of low boiling oils loses less thru volatilization on exposure to the sun and weather and is therefore less subject to change on standing and is to be preferred to road tars produced by the straight distillation of tar.

The attached drawing shows in a somewhat i diagrammatic manner apparatus for carrying out one embodiment of the invention.

The still 1 is provided with a vapor outlet connected thru. the pipe 2 with a condenser 3. In the condenser the vapors are sprayed with water or other cooling medium through spray nozzles 4. The distillate and unvolatilized cooling water are collected in the decanter 5. From the decanter the distillate can be separately recovered. A fractional condenser or other condensing means which may or may not be equipped with rectifying towers, etc., may be employed within the scope of this invention.

The still is heated by circulating hot oil thru coil 6. The temperature of the oil and the rate at which it is supplied to the still is regulated to supply sufficient heat to effect the distillation desired, and in addition to melt the solid pitch where, as in certain batch operations, the heat required for this purpose is not supplied entirely by the sensible heat of the contents of the still and the apparatus.

The tar to be distilled is introduced into the still through the line '7. A portion of the contents of the still are drawn off through the line 8 and at least a part of the material drawn oil is recirculated through the line 9 by means of the pump 10 and returned to the still through the same line through which the tar is introduced to the still, or a separate pipe may be provided for this purpose. When the operation is carried on as a continuous operation tar is added to the still continuously and a portion of the pitch product is drawn off of the still through the line 8 and out through the discharge 11 as the finished product and a part is recirculated through the line 9 and returned to the still. By circulating a portion of the contents of the still in this manner, circulation is kept up in the still and the contents of the still may be maintained in a relatively uniform condition. The solid pitch may be introduced through any suitable means such as the funnel 12, for example. The funnel may be provided with a rotary valve or other automatic means for supplying a constant supply of solid pitch to the still. The solid pitch mixes with and dissolves in the contents of the still and becomes thoroughly blended therewith.

Road tar may be produced from coke oven tar by distilling the tar to pitch with a melting point of 400 F. and then blending this pitch with a flux with an Engler viscosity of seconds (100 cc. at 100 C.) also produced by the distillation of coke oven tar. To produce road tar, such high melting point pitch and flux are blended in the proportions of about 18 parts of the high melt ing point pitch to 82 parts of flux.

To produce road tar from such pitch and flux in the still shown in the drawing, coke oven tar is added to the still until it is, for example, onehalf full or over as indicated by the level 13. The tar is distilled until flux with an Engler viscosity of 60 seconds (100 cc. at 100 C.) is produced, then solid pitch is added at a rate such that the temperature of the contents of the still does not increase and there is no substantial further distillation; this is continued until suiiicient solid pitch has been added to produce a pitch product comprising the desired proportion of high melting point pitch and flux. The rate at which the solid pitch is added is then reduced or the amount of heat supplied through the heating coils is increased or both the amount of solid pitch added and the amount of heat supplied through the heating coil are so adjusted that the temperature of the contents of the still is maintained such that there will be some distillation of the tar introduced into the still, and the vapors given off will be equivalent to the vapors produced on distilling the tar to flux with a viscosity of 60 seconds. The rate of the addition of tar and solid pitch to the still will be so regulated that each is added to the still in the proportion necessary to produce the road tar desired and road tar will be continuously drawn oil through the pipe 11 at the rate at which it is produced in the still.

By distilling tar to pitch of high melting point and then blending it with tar or pitch or" lower melting point to produce a blended pitch product such as road tar, a smaller amount of road tar and larger amounts of distillate are obtained than would be obtained by distilling tar by simple distillation methods to the melting point desired.

In the specification and in the claims by high melting point pitch, we mean a pitch with a melting point such that it can be crushed or ground or otherwise reduced to powder successfully on a commercial scale; as an example, pitch with a melting point of 300 F. or up to 400 F. or higher may be cited.

We claim:

1. The method of melting solid high melting point pitch which comprises introducing tar into a still, heating the still externally and distilling the tar and bringing the temperature of the contents of the still to a temperature such that the solid pitch will readily melt therein, introducing the solid pitch into the still and maintaining a considerable body of liquid within the still until the pitch is melted therein and continuously withdrawing a portion of the liquid contents of the still and returning it to the still at a different part of the still from which it was withdrawn.

2. The method of melting solid high melting point pitch which comprises introducing tar into a still, heating the still externally and distilling the tar and bringing the temperature of the contents of the still to a temperature such that the solid pitch will readily melt therein, introducing the solid pitch into the still and maintaining a considerable body of liquid within the still until the pitch is melted therein and circulating the contents of the still to maintain the contents of the still in a substantially uniform condition.

3. The method of preparing molten high melting point pitch from a solid comminuted high free-carbon pitch of the group consisting of comminuted high melting point coal tar pitch and comminuted high melting point water gas tar pitch, which comprises introducing tar into a still, applying heat to the tar so as to distill the tar forming hot liquid pitch at a temperature above the melting point of the solid pitch, maintaining in the still a substantial body of the hot liquid pitch, introducing the solid pitch into the still and intimately contacting it with the body of hot liquid pitch therein directly after its formation and while it is yet at a temperature above the melting point of the solid pitch, whereby the solid pitch is melted by the sensible heat of the liquid pitch and blended therewith.

4. The method of preparing molten high melting point pitch from a solid comminuted high free-carbon pitch of the group consisting of comminuted high melting point coal tar pitch and comminuted high melting point water gas tar pitch, which comprises continuously introducing tar into a still, applying heat to the tar so as to distill the tar forming hot liquid pitch at a temperature above the melting point of the solid pitch and maintaining a substantial body of the hot liquid pitch in the still, continuously introducing the solid pitch into the still and bringing it into intimate contact with the body of hot liquid pitch therein while distilling the tar to liquid pitch and while the liquid pitch so formed is yet at a temperature above the melting point of the solid pitch, whereby the solid pitch is melted by the sensible heat of the hot liquid pitch and blended therewith, and continuously withdrawing from the still the hot, liquid, blended pitch product.

5. The method of producing road tar from coke oven tar which comprises continuously addthe resulting flux blends with the high melting point pitch to produce a pitch product low in oils boiling below 355 C. and containing the free carbon from the pitch whereby said product is suitable for road tar, and continuously Withdrawing the product from the still.

S. P. MILLER.

M. L. HAMLIN. 

